Method of detecting an incident or the like on a portion of a route

ABSTRACT

A method for detecting an incident on a traffic lane uses a video camera having a target constituting an optoelectronic converter of a real optical image, the target being monitored by a programmable processing member and the incident detection process being designed to be carried out by activating the programmable processing member only when the real landscape image focused on the target is stationary. The inventive method includes detecting the beginning of displacement of the real image of the landscape relative to the target, in deactivating the programmable processing member right at the beginning of the displacement of the real image of the landscape relative to the target, and reactivating the programmable processing member at the end of the displacement of the real image of the landscape relative to the target to carry out the incident detection process.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage and claims priority fromPCT/FR03/02188 filed Jul. 11, 2003 which in turn claims priority fromFrench Patent Application 02/09521 filed Jul. 22, 2003 each incorporatedhere by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods of detecting changes in theoccupancy state of a portion of route suitable for being traveled alongby objects following its axis in a given scene, e.g. for the purpose ofevaluating variations in traffic density on the portion of route,methods which find a particularly advantageous application in the fieldof detecting incidents of any kind that might arise on the portion ofroute.

2. Description of the Related Art

Traffic, in particular motor vehicle traffic, has been increasingcontinuously over several years, and in certain circumstances, e.g.following an incident on the road used by such vehicles, congestionoccurs which undoubtedly impedes traffic flow. Proposals have thereforebeen made to remedy such drawbacks by detecting any incident that occurson a portion of route (in this case a portion of road) as quickly aspossible after it has occurred, and then controlling and modulatingvehicle traffic on said portion of road, and regardless of whether theportion of road is used by many vehicles (a traffic lane) or by fewvehicles (emergency stop lane, a zebra zone, a refuge, etc.).

In order to be able to detect such incidents, it is necessary to providesensors capable of giving an image of vehicle traffic on a portion ofroad. Numerous sensors have been developed. For example, a sensor hasbeen devised comprising photosensitive receivers associated with lightrays directed towards the roads along which vehicles are traveling andreturned by reflecting surfaces disposed for this purpose on theroadways, with the photosensitive receivers outputting signals each timea vehicle interrupts the light beams.

That technique gives good results. However the signals delivered arerepresentative of traffic at a determined point only, and the sensorsused are not flexible in use, since they require elements to be appliedto the roadway at locations that are well defined, and to ensure thatsaid reflecting surfaces reflect continuously by also providingartificial illumination when the lighting of the scene is low. Suchelements therefore cannot be moved without difficulty, and once theyhave been put into place, they require frequent intervention, if only tokeep their reflecting surfaces clean.

Other sensors have been made for increasing the area under surveillance.This applies to a sensor constituted by a magnetic loop embedded in theroadway. Such a sensor mitigates some of the above-mentioned drawbacks,but it remains too geographically restricted in use, specificallybecause it remains associated with a determined location of the roadwayand requires major roadworks for installation by sawing into theroadway.

A device has also been developed for implementing the method describedin EP-A-0 277 050. In that method, a main real image is initially formedof the portion of road in a plane that forms a non-zero angle with saidportion of road. This main image is then subdivided into a plurality ofpoints, and the relationship is determined between the size of a unitlength taken substantially at the portion of road and the size of itsimage formed in the main image, as a function of the number of pointscovered by the image and the location of the unit length on the portionof road. A secondary image is also determined in the main image, thesecondary image corresponding to a longitudinal mark associated with thevehicle on the portion of road, the different successive positions ofthe secondary image being defined by correlations with the number ofpoints covered by said secondary image, it being understood that saidsecondary image in said relationship corresponds to a constant length onthe portion of road.

The device described in that prior document gives very good results andmakes it possible to determine a very large number of parametersdefining traffic density on a portion of road. Nevertheless, it is veryexpensive or too complex for certain applications, thereby restrictinguse thereof.

A simpler device has also been developed such as that described in U.S.Pat. No. 4,258,351. That device comprises a series of photosensitivecells distributed in the focal plane of a converging lens. Each cell isconstituted by a strip, and each strip is designed so that its length isequal to the width of the image of the road formed by the lens. Saidlength thus complies with the perspective relationship for the road.

That technique presents the advantage of being easy to implement, but italso presents drawbacks: it requires an implementation for each road andonly one signal is obtained by lines crossing the road, thus making thesignals very difficult to interpret.

Other devices have been developed that give good results, constituted bya video camera having a target constituting an optoelectronic converterof an optical image, said target being controlled by a programmableprocessor member.

By way of example, such a device is described in FR-A-2 679 682, whichdiscloses an implementation of a method enabling an incident to bedetected on a portion of route situated in a scene when said portion ofroute is suitable for having objects traveling therealong.

Such a device presents advantages over the prior devices. In addition tobeing made out of elements that are commonly available, it enables theimages of the portion of route under surveillance to be stored in amemory, where such images can be used subsequently, e.g. to determinethe cause of an incident or the like that has occurred on said portionof route.

In addition, in order to be better aware of the nature and the immediateconsequences of an incident, thus making it possible to study the causethereof better, it is possible to modify at will the field of theobjective lens of the camera when it is constituted by a zoom lens,and/or to modify the direction in which the optical axis of the camerais pointing by mounting the camera to co-operate with a pointer memberso that the direction of its optical axis can be varied in elevation andin azimuth.

These facilities made possible by present video cameras are mostadvantageous for the operators of traffic routes, in particular roads,but they make it considerably more complicated to implement the methodof the kind given in FR-A-2 679 682 for detecting an incident using thetechnique referred to as “AID”.

The AID technique of Automatic Incident Detection on a portion of routecan be implemented only if the image of the portion of route formed onthe photosensitive target of the camera is stable for several seconds oreven several minutes, which it the time needed by the processor memberto execute the program for implementing the method. The method used inthat technique requires a manual calibration stage on a stable image. Ingeneral, the camera is held stationary and said stage is performed whenthe device is put into operation. For example, maintenance operations onthe camera make it necessary on each occasion to verify that the sensoris properly calibrated.

The method can therefore no longer be implemented when, for example, thedirection of the optical axis of the camera changes in elevation and/orazimuth, and/or when the field of the objective lens of the camera isvaried, e.g. by zooming into a particular area of the portion of routeand/or the scene that includes said portion of route.

The present invention thus seeks to implement a method which makes itpossible automatically to detect an incident that has occurred on aportion of route, e.g. using the AID technique described in FR-A-2 679682, even when the field of the camera lens has been modified, e.g. byzooming, and/or when the direction of the optical axis of the camera hasbeen changed in elevation and/or azimuth, and to do this without makingit necessary for technicians to intervene manually after each suchmodification, for example, while also making it possible to use thedevices for implementing prior art methods without needing to addadditional hardware means thereto.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method of detecting an incident on aportion of route situated in a scene when said portion of route issuitable for having objects traveling therealong, and when the methodmakes use of a video camera having a target constituting anoptoelectronic converter of a real optical image of the scene, saidtarget being controlled by a programmable processor member, the processfor detecting incidents being suitable for being performed by activatingsaid programmable processor member only while the real image of thescene focused on the target is stationary, the method beingcharacterized in that it consists:

-   -   in detecting the beginning of movement of the real image of the        scene relative to the target;    -   in deactivating the programmable processor member as soon as the        real image of the scene begins to move relative to the target;    -   in detecting the end of movement of the real image of the scene        relative to the target; and    -   in reactivating the programmable processor member at the end of        the movement of the real image of the scene relative to the        target in order to implement the process for detecting an        incident.

Other characteristics and advantages of the invention appear from thefollowing description given with reference to the accompanying drawingby way of non-limiting illustration.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole FIGURE is a block diagram of an embodiment of means forimplementing the method of the invention, and also serves to explain themethod.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method of detecting an incident on aportion of route 1 situated in a scene 2 when said portion of route issuitable for having objects of any kind traveling therealong, inparticular when it is a portion of road suitable for having motorvehicles traveling therealong.

The method is applied when a video camera 3 is used for implementing themethod, the camera having a target 4 constituting an optoelectronicconverter for converting a real optical image 5 of the scene 2, and whensaid camera is associated with means 14 for varying at will the field ofthe objective lens 15 of the camera when it is constituted by a zoomlens, and/or for changing the pointing direction of the optical axis 16of the camera so that the direction of said optical axis can becontrolled in elevation and in azimuth. These means 14 are themselveswell known and are therefore not described in greater detail herein inorder to simplify the present description.

The term “scene” is used to cover all of the elements of the scene inthe field of view of the camera, and not only the portion of route.

In addition, the target is analyzed by a programmable processor member 6such as a microprocessor or the like, optionally associated with anon-volatile memory 17 such as a video recorder or the like, withincidents on the portion of route 1 in the scene 2 being detectable onactivating the programmable processor member 6 only when the real image5 of the scene as focused on the target 4 is stationary.

The method of the invention thus consists in detecting the beginning ofany displacement of the real image 5 of the scene 2 relative to thetarget 4, in deactivating the programmable processor member 6 as soon asthe real image 5 of the scene begins to move relative to the target,then in detecting the end of the displacement of the real image of thescene relative to the target, and finally in reactivating theprogrammable processor member at the end of the displacement of the realimage 5 of the scene relative to the target 4 in order to implement theincident detection process on the portion of route 1.

In an advantageous first implementation of the method, the beginning andthe end of displacement of the real image of the scene relative to thetarget are detected by determining at least a first image point 10, 11,12, . . . in said real image 5 of the scene 2 that corresponds to afixed point 10′, 11′, 12′, . . . in the scene, and in generating a firstcommand signal when said first image point is subject to a change ofposition on the target 4, and then in controlling the programmableprocess member 6 as a function of said first command signal, i.e.initially deactivating the programmable processor member as soon as thereal image starts to move, and subsequently reactivating the sameprogrammable processor member at the end of the displacement of the realimage so as to perform the iterative detection process using thetechnique that is itself known.

In a second advantageous implementation of the method, the beginning andthe end of the displacement of the real image 5 of the scene 2 relativeto the target are detected by determining at least second and thirdimage points 10, 11, 12, . . . of the real image 5 of the scene 2corresponding respectively to two stationary points 10′, 11′, 12′, . . .of said scene, in generating a second command signal when the distancebetween said second and third image points is subjected to a variation,and subsequently controlling the programmable processor member 6 as afunction of the second command signal, i.e. initially deactivating theprogrammable processor member as soon as the real image begins to move,and then reactivating the same programmable processor member at the endof movement of the real image in order to perform the incident detectionprocess using the technique that is itself known.

In a third advantageous implementation of the method that will certainlybe preferred over the two preceding implementations, the beginning andthe end of movement of the real image of the scene relative to thetarget are detected initially by determining at least fourth and fifthimage points 10, 11, 12, . . . of the real image 5 of the scene 2corresponding respectively to two stationary points 10′, 11′, 12′, . . .of the scene, in generating a third command signal when the distancebetween the fourth and fifth image points is subjected to a change, orwhen at least one of the fourth and fifth image points is subjected to achange of position on the target 4, and in controlling the programmableprocessor member 6 as a function of the third command signal, i.e.initially deactivating the programmable processor member as soon as thereal image begins to move, and subsequently reactivating the sameprogrammable processor member at the end of the movement of the realimage so as to perform the incident detection process using thetechnique that is itself known.

It is specified that the above-defined command signals pass, forexample, from a first state to a second state when the beginning ofmovement of the real image 5 is detected, and from the second state backto the first state when the end of movement of said real image isdetected.

The programmable processor member 6 is deactivated throughout the periodduring which the command signal is in its second state.

For detecting incidents on a motor traffic road or the like, thestationary points 10′, 11′, 12′, . . . in the scene 2 may beconstituted, for example, by points that are dark (or particularlybright) on roadside signaling panels, lamp posts, or the like, portionsof advertising panels, or even points that are particularly dark (orparticularly bright) in given vegetation.

Detecting the beginning and the end either of movement of an image pointof the real image 5 of the scene 2 relative to the target, or ofvariation in the distance between two image points, can easily beimplemented, e.g. by means of the processor member 6 under the controlof a suitable computer program adapted to implement the method of theinvention, where writing such a program comes within the competence ofthe person skilled in the art who knows the above-explained method.

For easier and thus preferred implementation of the method, the target 4is made up of a plurality of photosensitive points, these photosensitivepoints being suitable for delivering signals that are a function of thequantity of radiation received on their photosensitive surfaces. Inaddition, the received surfaces of the photosensitive points areadvantageously of substantially the same dimensions. In fact,commercially available video cameras generally include such targets.

As mentioned above, an incident can be detected on the portion of route1 by activating the programmable processor member 6 only while the realimage 5 of the scene 2 that is focused on the target 4 is stationary.

When the programmable processor member 6 is activated, it is suitablefor detecting incidents on the portion of route using various processes.An advantageous example of one such process for detecting incidents,referred to as “AID”, is described and explained in FR-A-2 679 682, forexample.

In outline, that process for detecting incidents consists in selecting agroup of photosensitive points in the plurality of photosensitive pointsconstituting the target 4, said selected group of points correspondingto points on the portion of route 1 that are located on a plurality ofmain geometrical construction lines situated on the plane of the portionof route 1 and extending substantially parallel to the substantiallyrectilinear axis of the path along which objects normally travel on theportion of route 1, and in analyzing the sets of signals delivered bythe photosensitive points in the selected group.

This process for detecting an incident may also consist in subdividingthe selected group of photosensitive points into a plurality ofsubgroups of photosensitive points corresponding to points on theportion of route situated at the intersections between the mainconstruction lines and respective secondary geometrical constructionlines extending substantially perpendicularly to the main constructionlines, and in associating each photosensitive point of a subgroup with aweighting coefficient for multiplying the value of the signal emitted bysaid points, the weighting coefficients being a function of thepreferential probability of objects passing on the point on the portionof route whose image is the photosensitive point associated with theweighting coefficient.

The above-mentioned analysis of the signals delivered by thephotosensitive points can consist in averaging the values of the signalsdelivered at given instants by the points in each subgroup, and then foreach subgroup in comparing the averages obtained in this way and indeducing from the comparison whether an incident, if any, is present onthe portion of route.

The method of the invention as described and defined above can beexplained as follows.

Firstly, it is stated that it is easy to define the address of an imagepoint on the target of a video camera, particularly since said target ismade up of a plurality of photosensitive points such as pixels or thelike.

By analyzing said target using appropriate software that enables themethod of the invention to be implemented, it is possible automaticallyto monitor the position of an image point on the target. If the imagepoint is the image of a stationary point in the scene 2, then when thecamera moves in elevation and/or azimuth, the image point will changeits position. By tracking the changes in the position of the imagepoint, it is thus possible to determine the beginning and the end ofmovement of the real image of the scene 2 relative to the target, and todeactivate the processor member until the position of the image pointhas become stationary again.

When the image becomes stable again, i.e. when the image point isanalyzed as being stationary relative to the target, the processormember 6 again runs the process for detecting incidents using the AIDtype method as defined above.

Similarly, when the scene 2 is zoomed in or zoomed out, the image on thetarget will respectively become larger or smaller, and the same willtherefore apply to the distance between two image points.

In the same manner as described above, it is possible to determine thebeginning and the end of a zoom operation, and while it is taking place,to deactivate the processor member at least in part, with the portionthat remains active serving, for example, to watch for a return tostability.

Once the image has become stable again for a certain length of time asdetermined by the person skilled in the art, i.e. once two image pointsare analyzed as remaining at a constant distance apart, i.e. once theirrespective addresses have become stationary again, the processor member6 again runs the process for detecting incidents using the AID method asdefined above.

The above-described method is described using one image point fordetermining whether the camera is moving in elevation and/or azimuth,and two image points for detecting whether it is zooming in or zoomingout. However, in the application to detecting an incident on a portionof road for motor traffic or the like, it is advantageous to use alarger number of image points so as to be as certain as possible ofdetecting automatically any movement of the camera whether in elevationor in azimuth, and/or any zoom action. For example, it is not impossiblefor the position of an image point to be considered as stationary priorto a movement and for its position to be unsuitable for being consideredas stationary at the end of the movement, merely because the image pointthen belongs to the image of a vehicle moving along the portion of road1.

Thus, in order to lift this possible ambiguity, detecting the beginningand the end of movement of the real image of the scene relative to thetarget advantageously consists in defining a plurality of image pointsof the real image of the scene corresponding to a plurality of pointsthat are stationary at the beginning of movement of the real image, ingenerating a fourth command signal when some determined number of saidplurality of image points have become stationary again at the end ofmovement of the real image, and in controlling the programmableprocessor member as a function of said fourth command signal, i.e.initially deactivating the programmable processor member as soon as thereal image begins to move, and subsequently reactivating the sameprogrammable processor member at the end of movement of the real imagein order to implement the process for detecting an incident using thetechnique that is itself known.

The person skilled in the art knows how to determine the optimumquantity of image points to be used, and amongst said optimum quantityof image points, how to determine the number of stable image points thatshould be taken into account.

From the description given above, it can clearly be seen that the methodcan be implemented without manual intervention on the part oftechnicians every time there is a change in the pointing direction ofthe optical axis of the camera in elevation and/or azimuth, and/or everytime there is a change in the field angle of its objective lens, whilemaking use of the same devices as are used for implementing prior artmethods, and without it being necessary to add additional hardware meansthereto.

In order to implement the method of the present invention, it sufficesin conventional manner to load software adapted to the method into theprogrammable processor member, it being understood that writing suchsoftware comes within the competence of the person skilled in the art,as mentioned above.

1. A method of detecting an incident on a portion of route situated in ascene said portion of route is suitable for having objects travellingtherealong, and the method using a video camera controllable in one ofazimuth, elevation and field of view and having a target constituting anoptoelectronic converter of a real optical image of the scene, saidtarget being controlled by a programmable processor member, said processdetecting incidents comprising: A) having said programmable processingmember determine that said video camera is substantially stationary inrelation to said scene by i) selecting at least one point on a currentreal image of said scene, outside of said portion of said route; ii)comparing said at least one point on said current real image with saidat least one point on at least one of a set of immediate previoustargets of a stored image; iii) determining that said at least one pointis approximately at the same position in said current real image as inat least one of the set of immediate previous targets of the storedimage; iv)a) upon failure to determine the same position in step iii,re-execute steps i) through iii) with at least one other point; andiv)b) upon determining the same position in step iii), proceed to stepB) B) having said programmable processor member process said currentreal images to detect incidents.
 2. The method according to claim 1,wherein the real image of the scene beginning to move relative to thetarget occurs upon the beginning of a zooming in function or a zoomingout function of the real image.
 3. The method according to claim 1,wherein the end of the movement of the real image of the scene relativeto the target occurs upon an end of a zooming in function or a zoomingout function of the real image.
 4. The method of claim 1, wherein theprogrammable processor member is deactivated as soon as the stationarityof the scene relative to the target is detected as ending, andreactivated, in order to implement the process for detecting anincident, as soon as said stationarity of the scene relative to thetarget is detected as beginning.
 5. The method of claim 4, wherein saidbeginning and ending of said stationarity of the scene relative to thetarget are detected by determining at least one first image point ofsaid real image of the scene corresponding to a stationary point of saidscene, substantially outside said portion of said route, by generating afirst command signal when said first image point is subjected to achange of position of said target, and by controlling said programmableprocessor member as a function of said first command signal.
 6. Themethod of claim 5, wherein beginning and ending of said stationarity ofthe scene relative to the target are detected by determining at leastone second and one third image points of said real image of the scenecorresponding respectively to two stationary points of said scene,substantially outside said portion of said route, by generating a secondcommand signal when distance between said second and third image pointschanges, and by controlling said programmable processor member as afunction of said second command signal.
 7. The method of claim 6,wherein said beginning and ending of stationarity of the scene relativeto the target are detected by determining at least one fourth and onfifth image points of said real image of the scene correspondingrespectively to two stationary points of said scene, substantiallyoutside said portion of said route, by generating a third command signalwhen distance between said fourth and fifth image points changes, and bycontrolling said programmable processor member as a function of saidthird command signal.
 8. The method of claim 7, wherein said beginningand ending of stationarity of the scene relative to the target aredetected by determining a plurality of image points of said real imageof the scene corresponding to a plurality of points which are stationaryat the beginning of movement of said real image of the scene andsubstantially on said portion of the route, by generating a fourthcommand signal when a determined number of said plurality of imagepoints have become stationary again at the end of movement of said realimage of the scene, and by controlling said programmable processormember as a function of said fourth command signal.
 9. The method ofclaim 5, wherein said target is subdivided into a plurality ofphotosensitive points suitable for delivering signals as a function ofthe quantity of radiation received by their photosensitive surfaces. 10.The method of claim 6, wherein said target is subdivided into aplurality of photosensitive points suitable for delivering signals as afunction of the quantity of radiation received by their photosensitivesurfaces.
 11. The method of claim 7, wherein said target is subdividedinto a plurality of photosensitive points suitable for deliveringsignals as a function of the quantity of radiation received by theirphotosensitive surfaces.
 12. The method of claim 1, wherein said targetis subdivided into a plurality of photosensitive points suitable fordelivering signals as a function of the quantity of radiation receivedby their photosensitive surfaces.
 13. The method of claim 12, whereinthe process for detecting an incident on said portion of route when itis suitable for having objects traveling thereon along an axis andfollowing a path that is substantially imposed, comprises: in selectinga group of photosensitive points in said plurality of photosensitivepoints of the target, the selected group of points corresponding topoints of said portion of route located on a plurality of maingeometrical construction lines, said main construction lines beingsituated in the plane of said portion of route and all beingsubstantially parallel to the axis of said trajectory; and in analyzingthe set of signals delivered by the photosensitive points of saidselected group.
 14. The method of claim 13, wherein the detectionprocess further comprises: in subdividing said selected group ofphotosensitive points into a plurality of subgroups of photosensitivepoints corresponding to points on the portion of route situated at theintersections between said main construction lines and respectivesecondary geometrical construction lines that are substantiallyperpendicular to the main construction line; and in associating eachphotosensitive point of a subgroup with a weighting coefficient formultiplying the value of the signal emitted by said point, the weightingcoefficient being a function of the preferential probability of objectspassing over the point of the portion of route whose image is thephotosensitive point associated with said weighting coefficient.
 15. Themethod of claim 14, wherein the photosensitive receive areas of saidphotosensitive points are of substantially the same dimensions.
 16. Themethod of claim 15, wherein said analysis further comprises: averagingthe values of the signals delivered by the points of each subgroup atgiven instants; comparing the averages as obtained in this way for eachsubgroup; and deducing from said comparison the presence, if any, of anincident on said portion of route.
 17. An automatic road trafficincident detection system comprising at least one video camera with anoptical axis controllable in azimuth, elevation and focal distance, saidcamera being positioned alongside said road and fit for taking realimages of scenes of the road and converting them into target imageswhich are submitted as an entry to a computer process to detect trafficincidents, said computer process being deactivated by a programmableprocessing member based on detection of movement of the at least onevideo camera by the ending of stationarity of said target imagesrelative to said real images of scenes and being reactivated based ondetection of lack of movement of the at least one video camera by thebeginning of stationarity of said target images relative to real imagesof scenes, wherein said ending and beginning of stationarity of saidtarget images relative to said real images of scenes are detected byselecting at least one point on a current real image of said scenes,outside of said portion of said route, comparing said point on saidcurrent real image with said point on at least one of a set of immediateprevious targets of a stored image, determining that stationarity beginsupon said point being approximately at the same position in said currentreal image and said set of immediate previous targets of a stored imagerelative to said scene and that stationarity ends upon said point notbeing in the same position in said current real image and said set ofimmediate previous targets relative to said scene.
 18. A system fordetecting an incident in the flow of traffic, comprising: a camera withan optical axis controllable in azimuth, elevation and focal distancefor taking images of roadside scenes and transmitting them fordetermination of a roadside incident; and a programmable processorprogrammed to detect the roadside incident from images received from thecamera, wherein the programmed processor detects when the roadsideincident processing ends based upon a determination that the camera ismoving relative to a scene, the determination of camera movement basedupon changing points in a current live image relative to a set ofprevious images, the programmed processor detects the roadside incidentprocessing begins based upon a determination that the camera isstationary relative to the scene, the determination of camera movementbased upon points remaining fixed in the current live image relative tothe set of previous images.